Peculiarities of molecular-mass characteristicsт of copolymers synthesized in the presence of the triethylboron-oxygen system with varying time of introduction of butyl acrylate into boiling vinyl butyl ether

The copolymers of butyl acrylate with vinyl butyl ether were synthesized by dosing the active monomer in the presence of an oxidizing agent and triethylboron isolated from the complex with hexamethylenediamine in a solution of vinyl butyl ether by adding methacrylic acid in an amount proportional in moles to the amount of amine before introducing butyl acrylate. The triethylboron was oxidized by the air oxygen remaining in the reaction mixture during the boiling of vinyl butyl ether. The dosing of butyl acrylate was carried out at varying times: 20 minutes, 40 minutes and 60 minutes, and then the reaction mixture was thermostated for some time. At the end of the polymerization, the liquid fraction was distilled off. The obtained samples of copolymers, which were viscous, were dried; their conversion was evaluated by dry residue gravimetrically. Molecular weight parameters were determined for all samples by gel permeation chromatography. A differential refractometer R-403 (Å (Shimadzu) was used as a detector. Tetrahydrofuran was used as the eluent. Narrow-dispersed polystyrene standards were used for calibration. Polystyrene samples were converted to copolymer with the use of standard formulas for polystyrene samples. It has been shown immediately after finishing butyl acrylate dosing that copolymer molecular weight distribution curves are bimodal, oligomeric molecular weight distribution curves have low molecular mass (Mn less than 1000) and polydispersity coefficient (Mw/Mn)=1.1-1.2. Significantly larger low molecular weight modes have a molecular weight value ~ 30000, in all cases. Similar proportions for these two peaks are observed after thermostating the reaction mixtures after the introduction of butyl acrylate at the boiling point of vinyl butyl ether for another 20 minutes, the oligomeric curve of the molecular weight distribution of the first sample shifts in relation to that for the copolymer sample, selected immediately after dosing butyl acrylate for 20 minutes, and increasing the values of its molecular weight while maintaining polydispersity coefficient of 1.1. At the same time, for the other two samples, no shift in the molecular weight distribution is observed, as well as changes in the molecular weight values. In addition, the proportion of oligomer in relation to the low molecular weight polymer with a molecular weight of ~ 30000 decreases. Longer temperature control of the reaction mixture for two hours and more, after the end of dosing of butyl acrylate for both 40 and 60 minutes, unlike the process with dosing butyl acrylate for 20 minutes, also does not shift the molecular mass distribution curves of both peaks. This decreases the proportion of oligomeric peak in both cases.